Flexible overlay forming



1955 J. s. KIRKPATRICK ETAL 3,222,911

FLEXIBLE OVERLAY FORMING Filed April 16, 1962 5 Sheets-Sheet 1 INVENTORSJAMES S.K|RKPATRICK DONA D L.ERICKSON 1965 J. 5. KIRKPATRICK ETAL 3,

FLEXIBLE OVERLAY FORMING 3 Sheets-Sheet 2 Filed April 16, 1962 INVENTORS mm. m R m Mm 0 W w E A S l L 8mg E m xd J D /u 1965 J. 5.KIRKPATRICK ETAL 3,222,911

FLEXIBLE OVERLAY FORMING 3 Sheets-Sheet 5 Filed April 16, 1962 FIG FIG]INVENTORS JAMES S.K|RKPATR|GK DONALD L.ER|G K ATTORNEYS United StatesPatent 3,222,911 FLEXIBLE OVERLAY FORMING James Stanley Kirkpatrick andDonald L. Erickson, Dearborn, Mich., assignors to Brooks & Perkins,Inc., Detroit, Mich., a corporation of Delaware Filed Apr. 16, 1962,Ser. No. 187,673 9 Claims. (Cl. 72-363) The present invention relates toimprovements in a method of flexible overlay forming. More particularly,the invention deals with an improvement in certain metal stretching orso-called stretch-forming operations heretofore used in the making, fromsheet material, of specially contoured objects, most recently for use inthe aircraft industry. Such methods have involved the forming of sheetmetal blanks into a variety of different contoured shapes, compound orotherwise, by pulling the blank, either around a male forming member toconform the blank to the latter, or while the blank is between a set ofmale and female dies of a contour to provide a desired curvature,re-entrant or otherwise. The present improvements are of a characterdistinguishing from old established sheet forming procedures in a degreecomparable to other more recent types of forming, such aselectromagnetic forming, explosive forming, and the like.

It is commonly known that extreme and unusual material requirements havebeen imposed upon aerospace vehicles, due to extremely high aeronauticand astronautic operational temperatures and speeds. Materials aresubjected to temperatures ranging from the relatively low combustion andfriction-induced temperatures of normal aircraft to the tremendoustemperatures of re-entry and orbital vehicles. In order to form thesenew materials to various shapes many new techniques have been evolved inthe past few years, such as high energy procedures including impactforming, explosive forming, electromagnetic or electrostatic forming,cryogenic forming, etc., as mentioned above. Most of these techniquesare for relatively low quantities since to date the aerospace industryseldom requires more than a few prototypes or experimental units.

The materials desired to be formed, and the cost thereof, vary from suchrelatively common metals as steel and steel alloy sheet, aluminum,magnesium, and the like, obtainable at reasonable prices, to suchexotics as titanium, zirconium, hafnium, uranium, beryllium, columbium,molybdenum, etc., all at considerably higher prices. Some of thesematerials, for example certain ferrous alloys, columbium, etc., can beformed at room temperature, while others require the application ofheat, examples being magnesium, titanium, zirconium, hafnium, beryllium,molybdenum, etc.

Thus, some of these materials cannot be handled by conventionalprocedures at room temperatures because they are brittle and do notallow themselves to be gripped; they thus do not permit forming pressureto be applied thereto, as in conventional punch and die forming,stretchforming, and the like, without cracking.

A typical example of such a desirable material for use is beryllium. Itsrigidity is about twice that of the best steel and its weight iscomparable with that of magnesium. When melted, beryllium has a granularstructure characterized by a relatively enormous grain size up to inch,hence the metal is very brittle, indeed. It is produced in sheets bygrinding to a finely powered particle size, then sintering and rollingand/ or machining to form sheets. As thus produced the beryllium sheetobviously is very brittle, and has little bendability and tensilestrength such as are required by the stretch-forming method, anoperation strictly limited in use at normal operating temperatures bythe flexibility and pull strength of the material to be formed.

Generally considered, the present invention relates to an extension ofor improvement upon the metal forming procedure commonly known today asstretch-forming. In this operation, which may be carried outwith themetal in a hot or cold condition, depending upon its particular type, asheet or blank is supported by gripping the same at two opposite sides,or at spaced points around its periphery, and is then conformed undertension to a male punch element by a relative movement of the punch andsheet. In many instances a coacting female die is employed.

It is readily seen, in addition to the fact that the conventionalstretch-forming method may not lend itself practically to the productionof parts composed of the various materials noted above, that where thecost of such materials is so high as to be figured in dollars per squareinch, a saving of a few square inches area of the blank sheet to beformed may well amount to a considerable saving in the price of thefinal part. Thus, an elimination of the need for a considerable marginalarea, subsequently scrapped, at which the sheet is necessarily grippedin stretch-forming to hold the same against the forming member or punch,will result in a great saving of material cost for a run of even limitedsize.

It is further a fact that some of the new, exotic materials mentionedabove cannot be procured in pieces large enough to enable the formationof the part and still afford a flash zone to be gripped by thestretch-forming jaws.

Therefore, in accordance with the invention, the part is formed byemploying a flexible overlay or overwrap pressure applying sheet of anarea sufficiently greater than that of the sheet blank to be formed toenable the overlay sheet (as distinguished from the blank) to beconveniently gripped by the jaws of a conventional stretchformingmachine. The blank is interposed, in a cold or hot position, betweensuch overlay sheet and the punch, about which punch it is then shapedthrough the action of the tensioned overlay.

This type of secondary or pressure wrap forming procedure enables thematerial of the production sheet or blank to be maintained at anabsolute minimum area by eliminating the need for a direct grip thereofby the stretch-forming jaws.

Another object is to provide for the use of a flexible overlay sheet inthe forming of metals, as described above, in which, in addition to asaving of material cost and avoiding the drawback of brittleness, theprocedure en-- ables the formation of materials which would be so soft,if subjected to conventional stretch-forming tension, as to be unable topull themselves onto the contour of a punch, even if not being toobrittle to permit this action.

The procedure also enables the formation of materials, such as theexotic ones, which are not weldable, so that the technique of weldinggripper jaw material to the blank to be formed is not practical.

A further object is to provide a procedure which enables the overlaysheet to which forming pressure or tension is applied to be of not onlya higher strength and 3 much less expensive material than the materialbeing formed, but also of a resilient, flexible or ductile characterhaving no tendency to fracture under tensile or bending stress.

As indicated above, the invention contemplates a procedure which may beused efiectively for either the hotforming or cold-forming of sheets.Moreover, the overlay member may, if desired, be chosen of a suitablematerial to act as a resistance heating element to heat the part beingformed.

Materials which may be termed reactive, in the sense that they cannot beformed in the atmosphere at elevated temperatures due to oxidation, butmust be formed under heat in a non-reactive or inert surrounding, may insome cases be formed by the improved procedure, since in such 'cases iteliminates the need for heating to impart required forming ductility.The invention also lends itself to the production of forms from othermaterials as to which the temperature of forming may tend to impose alimitation on the practicality of following known forming techniques.

Yet another object is to provide a procedure which, employing as it doesa flexible overlay sheet to exert direct forming pressure on thematerial to be formed, permits this pressure to be maintained while theformed part takes a set or cools, thereby eliminating spring-back.

Similarly, the flexible overlay procedure permits the insertion ofsuitable auxiliary pads of rubber or the like in supplementation of theoverlay sheet to force certain contours into the part being formedagainst a forming member.

A further object is to provide a procedure of overlay forming of sheets,as described, wherein the overlay sheet may be provided with holesdrilled therethrough adjacent a margin thereof, or with marginal or edgenotches or the like, enabling the formation of locating holes orindentations on the formed piece. Such formations might, for example, besubsequently employed for reference in the location of a template overthe formed workpiece, with the assistance of which template the piece isthen trimmed to its final desired shape.

A still further object is to provide a procedure whereby afinishedworkpiece may be re-set to final shape between the overlay sheetand the member or punch against which the workpiece was initiallyformed, in the event the workpiece has been machined or otherwisehandled in a manner which might tend to distort it.

It is further an object of the invention to provide a method wherein theoverlay forming sheet and punch may be supplemented by the provision ofrollers coacting with the sheet to more effectively force the same andthe workpiece against certain portions of the punch to con form to thelatter, for example, in a zone at which tension on the overlay sheetmight not normally be expected to exert, of itself, a sufiicient forcenormal to the surface of the sheet to cause efficient forming.

The foregoing as well as other objects will become more apparent as thisdescription proceeds, especially when considered in connection with theaccompanying drawings illustrating preferred embodiments of theinvention, wherein:

FIG. 1 is a fragmentary and highly schematic view in elevationillustrating suitable means for carrying out the improved method in aknown type of vertically acting press of a sort employed in astretch-forming operation, the view showing in dot-dash line the initialfiat sheet metal blank to be formed and indicating in dotted line thesaving of material made possible by the improved procedure;

FIG. 2 is a similar fragmentary view showing a slight modification inregard to the equipment of FIG. 1, involving the use of auxiliarymechanical sheet forming or ironing means in association with the pressstructure of FIG. 1;

FIG. 3 is a fragmentary schematic top plan view illustrating the mannerof conducting the improved method using a horizontal stretch type ofpress embodying hydraulic gripper jaws;

FIG. 4 is a fragmentary view in axial section showing permissivemodifications of the improved overlay type of forming in the productionof contoured products having special protuberant or re-entrant formfeatures;

FIG. 5 is a fragmentary schematic view illustrating the manner in whichthe method may be carried out on a standard single action hydraulicpress, as distinguished from the preceding types more specially utilizedin the aerospace industry;

FIG. 6 is a fragmentary view similar to FIG. 5 illustratingmodifications contemplated by the invention to permit the making ofcertain template register formations on the formed product; and

FIG. 7 is a fragmentary schematic view illustrating the mode ofperforming the improved method upon a standard type of industrialdouble-action press.

In reference to FIGS. 1, 3, 5 and 7, showing various types of basic,mechanically or hydraulically operated press equipment commonly employedin the sheet metal forming industry, whether in aerospace or lessspecialized production, it is to be understood that the further specialfeatures of improvement or refinement specifically illustrated in FIGS,2, 4 and 6 (to be described) are available for use with completeinterchangeability or optionality and in common with the basic equipmentof FIGS. 1, 3, 5 and 7, as with other known types not shown. That is, innone of the refinements appearing separately in FIGS. 2, 4 and 6 arethese features mutually exclusive of one another, or to be considered asparticularly special to the particular type of equipment with which theyare shown associated. Obviously, to illustrate and describe each featurein all possible combinations with other subordinate features would in ahighly undesirable way, and unnecessarily, complicate the disclosure.

In particular reference to the equipment of FIG. 1, it is schematicallyshown as a vertically acting stretchforming type of press 10 as employedin the aircraft and aerospace industry, featuring a ram 11 mounted onthe plunger 12 of a hydraulic cylinder (not shown) to be elevated andlowered by the plunger. In certain later models of this equipment theram is operated in a horizontal direction; and in standard types of highproduction mechanical presses, of more general application, the ram 11is driven downwardly by appropriate mechanical or hydraulic means.

In known methods of stretch-forming, a sheet of appropriately contouredmetal .to be formed is gripped about its periphery or at its edges by aseries of pairs of gripper jaws, of the sort designated 14 in FIG. 1,being held "by these jaws while an appropriately contoured male formingblock or punch l5, secured on ram 11, isurged against the thus anchoredsheet. As indicated above, this requires a sheet blank of considerablesize to provide necessary marginalgrippingarea, as well as a sheet ofconsiderable ductility and, tensile strength to withstand the bendingandtension stress of stretch-forming. The formed sheet is subsequentlytrimmed from the sheet blank, with a wastage of the trimmed materialamounting to a substantial area permitting its grip by the jaws 14; andthis is the case even'if the material of the sheet is sufficientlynon-brittleand strong to permit of conventional stretchforming.

In accordance with the improvement of the invention, the sheet to beformed, shown in dot-dash line and designated 16, is initially fiat andof a shape and area but little, if any, greater than that of thefinished product (specially designated P in FIG. 1). This is showntypically as being a portion of a semi-cylinder, which is theillustrated shape of the male forming block member or punch 15.

The reference numeral 18 designates an overlay sheet of substantiallygreater area than that of the sheet 16 to be formed, and fabricated of amaterial not only greater in tensile strength and flexibility than thesheet 16, but also less expensive usually in nature. In accordance withthe invention the overlay sheet 18 may be of a suitable grade of steel,steel alloy, non-ferrous metal or other material appropriate to thepurpose.

The male forming block 15 may be suitably heated, in the event theprocess has to be carried out at elevated temperature due to acharacteristic of the sheet 16. Heating may be by electrical resistancethrough inserted elec trical units (not shown), or by gas ringcombustion of a gas, or the like. As indicated above, the overlay sheet18 may itself be employed as a resistance element for the purpose insome instances, if fabricated of a suitable electrically resistivematerial.

With the sheet 16 laid over the forming block in flat form, as indicatedin dot-dash line in FIG. 1, the overlay sheet 18 is applied over thesame and, being gripped by pairs of jaws 14 or a series of such pairsabout the edge of the sheet '18, the latter is caused to exert formingpressure on sheet 18 as the punch or block 15 is advanced upwardly. Thisoperation is carried out until sheet 16 is contoured finally to form theproduct P in a set condition, ready for a further marginal trimming orother operation thereon.

FIG. 1 graphically depicts the economic desirability of the improvedmethod, whether as performed by the equipment of FIG. 1 or by that ofother figures to be described. As shown in dotted line in FIG. 1, thereis a savingof otherwise scrapped stock represented in area by thelongitudinal dimension S times its width or circumferential extent,possibly of a very expensive material, which would be required in theconventional stretchforming procedure (even were that procedurepermissible for the forming of such material); and the need for thiswastage is eliminated by the utilization of the stretchforming sheet 18.Such material is normally trimmed from the finished part or product in alater stage of the production, and because the trimmed-off material hasbeen greatly reduced in length as compared with the dimension of theoriginal blank it is of course no longer available as a standard blanksize for a further forming operation.

It has been proposed to weld suitable gripper jaw material to the partto be formed in order to permit of the conventional stretch-formingoperation. However, this is in many cases not practical for thetechnical reasons that many of the new materials presently referred toas exotic materials are not weldable, as well as being too expensive tojustify wastage arising from welding.

It may be found desirable, as illustrated in FIG. 2

'of the drawings, to supplement the pressure exerted by the overlaysheet under tension in the forming of the product P, in order to buildup a forming force on the blank 16 which the overlay sheet 18 possiblycould not exert against the sheet, in certain areas thereof, in adirection at 90 to its surface. This can be done, for example, by theuse of opposed forming or ironing rollers 20. These may be resilientlyspring-urged, or otherwise yieldably urged, against the overlay sheet 18during the forming operation, for the purpose of amplifying the direct,radially effective forming force on the overlay sheet 18, and, throughit, upon the form product P.

Furthermore, if it is desired, provision may be made for producing aflat or re-entrant or other special surface contour on the product P, asby providing one or more flats or grooves 21 on the male punch or block,with the pressure applied through the overlay sheet 18 (alone or assupplemented by the ironing means 20) causing the sheet blank 16 tocontour itself properly against such special surface or surfaces 21.

FIG. 3 of the drawings shows the overlay sheet forming technique asperformed with the use of a horizontally acting hydraulic stretch press22. This press features hydraulically operated gripper jaws 23 clampingthe overlay forming sheet 18at its edge, the opening and closing of thejaws being controlled concurrently with the operation of a hydraulicplunger 24, which urges the forming punch head or block 15 to the left,as viewed in FIG. 3. Block 15 is mounted fixedly to the horizonta'llyacting ram 25. Many types of gripper jaws 23 are available in horizontalstretch presses of the sort shown in FIG. 3.

FIG. 4 of the drawings illustrates a further refinement according to theinvention, by recourse to which other special or non-symmetric productsmay be formed by practicing the method of the invention. Thus, should itbe desired to form a product, specially designated P (lower portion ofFIG. 4) having one or more cavities or re-entrant formations 27 therein,the forming member (specially designated 15') is contoured to provide amating concavity or depression 28; into which formation the material ofthe sheet blank to be formed is forced by interposing a suitable rigidor non-rigid auxiliary filler or adapter 29 between the blank sheet andthe overlay sheet 18. The latter acts on the exterior of the piece 29 toproduce requisite forming force.

By the same token, and again referring to FIG. 4, a product P" may beformed featuring one or more special protuberances 31 by interposing oneor more special, similarly conformed auxiliary make-up, filler or shimpieces 32 between the normally contoured surface of the male punch 15and the overlay sheet 18.

FIG. 5 shows the application of the basic principles of the invention toforming through the agency of a standard industrial press, which may bemechanically or hydraulically operated. It comprises a fixed, massivebolster plate 35 disposed horizontally and :provided with upright presscolumns 36, upon which the movable press head plate 37 guided for up anddown action, being operated through the usual hydraulically ormechanically actuated press ram 38.

A suitable material forming block or punch 15 is fixedly secured to amounting member 40 and spacer 41 fixed on bolster plate 35. The pressurehead 37 sustains a jaw carrying member 43 provided with suitable jaws 44to grip the edge of the overlay forming sheet 18; and thereby form theproduct P as the press plate 37 and member 43 carry the jaws 44downwardly relative to the male forming punch or block 15.

It is usually desirable to perform subsequent trimming or likeoperations upon the formed product P, in turn requiring accuratetemplate register of the latter in relation to the trimming or likeoperating instrumentalities. Therefore, in accordance with the inventionas illustrated in FIG. 6, it may be desirable to form the male punchmember or block, designated 15", with one or more radial holes 46extending laterally therein (lefthand side of FIG. 6); and to similarlyform the overlay sheet, here specially designated 18, with acorresponding number of apertures 47, through which a suitable tool (notshown) may be driven into the apertures 46 to form register openings inthe product P adjacent or around its free edge.

Referring to the right-hand side of FIG. 6, an alternative provision isrepresented by the provision of means to form marginal serrations orregister notches on the product, for example by the provision ofappropriate formations 49 on the block 15 to coact with a marking toolapplied to the exterior of the overlay sheet at openings of the latter.

FIG. 7 of the drawing illustrates an adaptation of the improved processto be carried out using a standard industrial double-action press,designated 51, wherein the function of the gripper jaws of the precedingembodiments is performed by certain coacting parts of the press.

Here, the press 51 comprises a fixed horizontal bottom bolster 52,upright press columns 53, and a first action ram-actuated press plate54, guided by the columns 53 for vertical up and down movement. Plate 54is driven by a first action or ram component 55; and a second action orcomponent of the press is constituted by the gripper heads 56, which aresuitably guided for movement relative to the press plate 54. The maleforming tool, blockor punch 15 is fixedly mounted in depending relationto press plate 54; and the bolster 52 is equipped with upright grippingposts 58 aligned with and adapted to coact with the gripper heads 56.

In the operation of the dual-acting press 51, the gripping heads 56 arefirst advanced downwardly to grip the overlay sheet 18 tightly againstthe respective fixed gripping posts 58 on bolster 52. Thereupon, thefirst ram compoment or action 55 drive press plate 54 and forming block15 downwardly against the material to be formed, as interposed betweenoverlay sheet 18 and the contoured surface of block 15. As in all otherembodiments, the equipment of FIG. 7 may be operated hot or cold,depending upon the requirements of the product P being formed.

In any of these embodiments the tensile force applied to overlay sheetmay range from to 500 tons.

It is seen from the foregoing that the illustrated and described processpermits the formation to special contoured shapes of certain materialsthat to the best of our knowledge have not heretofore been formable byother techniques; that the method in enabling even a few square inchesto be saved on each workpiece, can result in a great price reduction ofthe final part; and that the method permits the working of certain newmaterials which cannot even be procured in pieces large enough to form apart by conventional stretch-forming, leaving still a flash or stretchjaw zone available.

Further the improved technique enables the forming of material whichwould fail and be unable to be pulled onto a punch contour when theedges are gripped'by another type. The material of the overlay sheet mayoften be of a much 'less expensive material than that formed, just as itis ordinarily of much higher strength and more ductile as compared witha brittle part being formed.

The process can be used effectively either for hotforming or for coldforming, with the possibility that the overlay member being used mayalso act as a resistance element furnishing heat to the operation ifsuch is required.

Under appropriate circumstances, rigid or resilient inserts, adapters orpads can be put under the material doing the work to force certaincontours into the part being formed; and the process can be adapted tomany existing standard pressure exerting tools, or may be carried out bya specially designed type of tool or equipment.

The drawings and the foregoing specification constitute a description ofthe improved flexible overlay forming in such full, clear, concise andexact terms as to enable any person skilled in the art to practice theinvention the scope of which is indicated by the appended claims.

What we claim as our invention is:

1. A method of forming a metal sheet blank into an object of non-planarshaped cross sectional contour, comprising providing a rigid formingmember of a contour generally corresponding to the desired objectcontour, providing a flexible metal overlay sheet of an area exceedingthat of said blank in the portion thereof desired to be contoured,disposing said sheet blank in a position between said forming member andoverlay sheet to be covered by the latter at said portion, causing saidoverlay sheet to be tensioned from points outwardly of said portion soas to Wrap and conform said sheet and sheet blank about said formingmember, and said blank sheet to assume and retain said cross sectionalcontour as an object so conformed, and employing said overlay sheet toform a register mark upon the conformed object while the latter ispositioned between said overlay sheet and forming member, bymanipulating a tool from the exterior of said overlay sheet to form aregister indicium on said object.

2. A method in accordance with claim 1, in which the manipulation ofsaid tool involves the positioning of said tool relative to said objectby reference to said overlay sheet.

3. A method in accordance with claim 1, in which the manipulation ofsaid tool involves the thrusting of the same through an opening of saidoverlay sheet.

4. A method in accordance with claim 1, in which the manipulation ofsaid tool involves the thrusting of the same through an opening of saidoverlay sheet and into the material of said object to provide saidindicium.

5. A method in accordance with claim 1, in which the manipulation ofsaid tool involves the thrusting of the same through an opening of saidoverlay sheet and into the material of said object in spaced relation toa margin of the latter to provide said indicium.

6. A method in accordance with claim 1, in which the manipulation ofsaid tool involves notching of a margin of said object by a toolpositioned relative to the object by reference to said overlay sheet.

7. A method of forming a metal sheet blank into an object of anon-planar shaped cross sectional contour, comprising providing a rigidforming member of a contour generally corresponding to the desiredobject contour, providing a flexible metal overlay sheet of an areaexceeding that of said blank in the portion thereof desired to becontoured, disposing said sheet blank in a position between said formingmember and overlay sheet to be covered by the latter at said portion,causing said overlay sheet to be tensioned from points outwardly of saidportion so as -to wrap and conform said sheet and sheet blank about saidforming member, and said blank sheet to assume and retain said crosssectional contour as an object so conformed, and employing said formingmember to form a register mark upon the conformed object while thelatter is positioned between said overlay sheet and forming member, bymanipulating a tool from the exterior of said overlay sheet to form aregisterindicium on said object.

8. A method of forming a metal sheet blank into an object of anon-planar shaped cross sectional contour, comprising providing a rigidforming member of a contour generally corresponding to the desiredobject contour, providing a flexible metal overlay sheet of an areaexceeding that of said blank in theportion thereof desired to becontoured, disposing said sheet blank in a position between said formingmember and overlay sheet to be covered by the latter at said portion,causing said overlay sheet to be tensioned from points outwardly of saidportion so as to wrap and conform said sheet and sheet blank about saidforming member, and said blank sheet to assume and retain said crosssectional contour as an object so conformed, and employing said overlaysheet and forming member in coaction withone another to form a registermark upon the conformed object while the latter is positioned betweensaid overlay sheet and forming member, by manipulating a tool from theexterior of said overlay sheet to form a register indicium on saidobject.

9. A method of forming a metal sheet blank into an object of anonwplanar shaped cross sectional contour, comprising providing a rigidforming member of a contour generally corresponding to the desiredobject contour, providing a flexible metal overlay sheet of an areaexceeding that of said blank in the portion thereof desired to becontoured, disposing said sheet blank in a position between said formingmember and overlay sheet to be covered by the latter at said portion,causing said overlay sheet to be tensioned from points outwardly of saidportion so as to wrap and conform said sheet and sheet blank about saidforming member, and said blank sheet to assume and retain said crosssectional contour as an object so conformed, and employing said overlaysheet and forming member in coaction with one another to form a registermark upon the conformed object adjacent a margin 9f the latter while thelatter is positioned References Cited by the Examiner UNITED STATESPATENTS 7/1923 Bancroft. 3/1942 Chamber 15340 Berliner et a1 153-32Berger et a1. 153-48 Smith 1534O Faeber et a1.

Homer 15348 CHARLES W. LANHAM, Primary Examiner.

1. A METHOD OF FORMING A METAL SHEET BLANK INTO AN OBJECT OF NON-PLANAR SHAPED CROSS SECTIONAL CONTOUR, COMPRISING PROVIDING A RIGID FORMING MEMBER OF A CONTOUR GENERALLY CORRESPONDING TO THE DESIRED OBJECT CONTOUR, PROVIDING A FLEXIBLE METAL OVERLAY SHEET OF AN AREA EXCEEDING THAT OF SAID BLANK IN THE PORTION THEREOF DESIRED TO BE CONTOURED, DISPOSING SAID SHEET BLANK IN A POSITION BETWEEN SAID FORMING MEMBER AND OVERLAY SHEET TO BE COVERED BY THE LATTER AT SAID PORTION, CAUSING SAID OVERLAY SHEET TO BE TENSIONED FROM POINT, OUTWARDLY OF SAID PORTION SO AS TO WRAP AND CONFORM SAID SHEET AND SHEET BLANK ABOUT SAID FORMING MEMBER, AND SAID BLANK SHEET TO ASSUME AND RETAIN SAID CROSS SECTIONAL CONTOUR AS AN OBJECT SO CONFORMED, AND EMPLOYING SAID OVERLAY SHEET TO FORM A REGISTER MARK UPON THE CONFORMED OBJECT WHILE THE LATTER IS POSITIONED BETWEEN SAID OVERLAY SHEET AND FORMING MEMBER, BY MANIPULATING A TOOL FROM THE EXTERIOR OF SAID OVERLAY SHEET TO FORM A REGISTER INDICIUM ON SAID OBJECT. 